This invention relates generally to wireless one-way communication systems and more particularly to a transmission and reception protocol that increases battery life in data receivers while maintaining reliable data transmission.
Radio paging devices and protocols are presently utilized in commercial paging networks to transmit short messages of around ten characters or less. For example, U.S. Pat. No. 4,713,808 to Gaskill et al., describes a paging system and protocol that transmits messages to a portable paging receiver. To extend battery life, the paging receiver periodically polls for data transmitted during specific time slots in a time division multiplexed (TDM) data stream.
Since the paging receiver is activated only in bursts for brief periods of time, little power is needed to operate the receiver over an extended period of time. Thus, batteries used in the receiver typically operate for up to one year.
Polling a data channel in brief time bursts is an efficient means for transmitting and receiving short messages. However, this communication protocol is not as effective when transmitting long messages of more than ten or twenty characters. For example, U.S. Pat. No. 4,713,808 describes a (TDM) data protocol where messages are queued into time slots and multiplexed together to form data frames. A receiver then polls the data frame during discrete time instances, such as once every few minutes.
The receiver is synchronized with the transmitter so that any message directed to the receiver will be transmitted at the same time that the receiver is turned on. If an address contained in the time slot is the same as an assigned address of the receiver, a data packet contained in the time slot is targeted for that receiver. The receiver will then read the data packet and output the messages contained in the data packet.
If the message is long, for example, more than ten characters, it cannot be contained within the single data packet of a time slot. Thus, the entire message must be transmitted by sending several portions of the message over several time slots. The receiver polling rate, however, is too slow to transmit the long message in a time efficient manner. For example, if the receiver only polls for messages once every two minutes, a long message extending over say five time slots would take at least ten minutes to transmit. In addition, messages are typically transmitted several times to ensure message reception. Thus, the time required to transmit the long message would be further increased several times.
If the polling rate of the receiver is increased to reduce the amount of time required to send a long message, the operating life of the batteries used for operating the receiver is proportionately reduced. Alternatively, long message transmission rates could be increased by eliminating transmission of redundant data. However, eliminating message redundancy reduces data transmission reliability and increases the probability that messages will not be accurately transmitted and received.
Accordingly, a need remains for quickly and reliably transmitting and receiving long messages while maintaining low receiver power consumption.